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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Gravitational differentiation due to initial chemical stratification: origin of lunar asymmetry by the creep of dense KREEP?
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Gravitational differentiation due to initial chemical stratification: origin of lunar asymmetry by the creep of dense KREEP?

机译：初始化学分层引起的引力分化：致密KREEP蠕变引起的月球不对称性起源？

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Models for the evolution of the Moon must explain a number of important characteristics of its magmatic history. Primary among them is the emplacement of mare basalts primarily on one side of the Moon, and in a region of the surface roughly correlating with that containing high subsurface concentrations of KREEP. It is thus important to explore mechanisms which will regionally concentrate a KREEP layer early in lunar evolution and which ～400-500 Myr later give rise to mare basalt generation beneath the same region. Gravitational instability of a chemically dense, ilmenite-rich cumulate created during the fractionation of an anorthositic crust is one candidate model. It so, gravitational instability must occur at long wavelength to explain the hemispheric asymmetry. We examine the Rayleigh-Taylor instability of a dense layer near the surface of a sphere, representing the lunar mantle, in which the viscosity varies with depth. Our results show that spherical harmonic degree 1 is the fastest growing wavelength of instability if the viscosity of the dense layer is sufficiently low relative to that of the deeper mantle or if the viscosity of the mantle increases with depth. However, the viscosity increase cannot be distributed over a depth that is too large. We explore whether a residual KREEP-like layer near the base of anorthositic crust might give rise to these needed conditions.
机译：月球演化的模型必须解释其岩浆历史的许多重要特征。其中最主要的是将母玄武岩主要放置在月球的一侧，并在其表面区域与含有较高地下KREEP浓度的区域大致相关。因此，重要的是要探索一些机制，这些机制将在月球演化的早期集中区域性地形成一个KREEP层，然后在〜400-500 Myr之后在同一区域下产生母马玄武岩。一种化学模型致密，富含钛铁矿的堆积物的重力失稳是一种候选模型，该物质在分离无花果皮时产生。因此，重力不稳定性必须在长波长下发生，以解释半球不对称性。我们检查了代表月球地幔的球体表面附近致密层的瑞利-泰勒不稳定性，其中粘度随深度变化。我们的结果表明，如果致密层的粘度相对于较深地幔的粘度足够低，或者如果地幔的粘度随深度增加，球形调和度1是不稳定性增长最快的波长。但是，粘度增加不能分布在太大的深度上。我们探讨了在正畸硬皮基部附近残留的类似KREEP的层是否会引起这些必要条件。

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